This was Nas just being deep, meaning he had love for Biggie on some brother/fellow Black Man shyt. He would say he loved Jay right before he would perform Ether at concerts
Anyway, heart is not used by the common male New Yorker in relation to other males in NY.
The trendy word to refer to other males now is "bro".
That “my heart” shyt is new probably started right before the pandemic type shyt
It’s meant in the same way Nas meant in there
The slang for a close friend is “my heart”, “gang”, or “muddy”
It’s more of a Gen Z NY street lingo so the
gonna be confused
Also depends if you’re gang affiliated SMM members refer to each other as “trends”, Makk Ballas as “sleaze” and Crips as “‘rips” and so on
That “bro” shyt been going on for a minute and we always said “bro” even when other regions was saying “bruh” we never used that like that
NY street lingo always been kinda sus I mean that “baby” and “daddy” shyt came from Harlem dudes in the 40’s and 50’s
Beloved is some shyt millennial generation came up with particularly UBN members I’ll give Taxstone credit for that for using it on his podcast and being a big Twitter dude it’s not used like that anymore only by endearing 40 year old dudes who also call dudes “king” lol
Dominicans don't call other Dominicans papi. Puerto Ricans do that. 
